The invention relates to a steering gear for a rack and pinion steering system.
Nowadays, rack and pinion steering gears are used almost exclusively in vehicle steering systems, in particular in cars. These steering gears comprise a steering rack which is guided for displacement in a housing along its axis, and a pinion which meshes with a serrated section of the steering rack and is connected to a steering wheel by means of a steering rod. The two axial ends of the steering rack project from the housing and are each joined to a tie rod by a ball joint, the tie rod being coupled with a vehicle wheel.
Viewed in the direction of the steering rack, the pinion is generally located closer to one end of the housing than to the other end. The axially displaceable mounting and guiding of the steering rack is generally implemented at two points in the housing, one of them at the end of the housing remote from the pinion, and the other directly at the point of contact of the pinion where a pressure piece acts upon the steering rack in the direction of the pinion. By means of this two-point mounting, the steering rack is mounted in a statically determinate manner, and this contributes to the lightness of steering; any further mounting position would lead to a static over-determination, and so possibly to tensions.
One problem with this arrangement is the relatively large distance between the mounting position on the pinion and the point of contact of the tie rod at the end of the steering rack near to the pinion. Because the force which is introduced into the tie rod or from the tie rod into the steering rack, generally also has a component which does not run in the longitudinal direction of the steering rack, this leads to a bending load which acts on the steering rack.
An extreme bending load applied to the steering rack occurs, for example if, when the steering is operated, the tire is blocked in its steering movement (e.g. by a curb). The dimensioning of the steering rack is significantly affected by this type of extreme case of bending load.